Volume control



April 22, 1930; Q s. TARZIAN 1,755,310

VOLUME CONTROL Filed Nov. 19, 1927 TEMPERA RE PLATE. cumzsm' MW M214 @2511 Patented Apr. 22, 1930 UNITED STATES PATENT OFFICE MANUFAGTURING COMPANY, OF PHILADELPHIA, PENNSYLVANIA, A CORPORA- MON 01? PENNSYLVANIA VOLUME conrnor.

Application filed November 19, 1927. Serial No. 234,847.

My invention relates to the control of the volume or amplitude of si als, music or speech as reproduced by radlo receiving apparatus, and especially such as involves high degrees of amplification, and particularly in which the cathodes or filaments of the thernionic vacuum tubes are heated, by alternatng current. In accordance with my invention there is utilized, in one ormore stages of radio frefilaments or cathodes are heated b alternating current, a capacity, varia le either smoothly or in steps, and so electrically positioned or related to the amplifier circuits that the amplification ma be materiallyreduced when receiving rom powerful or nearby broadcasting stations, and restored when receiving from distant or less powerful stations.

More particularly in accordance with my invention the variable capacity is so connected in the output system or plate circuit of an amplifier that the difference of potential effectively impressed upon the means for coupling the amplifier to the succeeding circuit or stage may be reduced and the effective resistance of theinput system of the amplifier increased, materially to reduce the amplification and thereby the volume or amplitude of the reproduced signal, speech or mu- More particularly in accordance with my invention a variable capacity is connected between the high potential terminal of the primary of an' output coupling transformer and the anode or plate of the amplifier.

Further in accordance with my invention the variable capacity-is suitably related to a circuit of an amplifier between whose input and output circuits or systems exists undesired capacitative coupling which is more or less neutralized.

Myinvention resides in a volume control quency amplification, particularly where the of the character hereinafter described and claimed.

For an understanding of m invention and for an illustration of some 0 the various forms it may take reference is had to the accompanying drawing in which:

Fig. 1 is a diagrammatic view of a radio receiving system embodying my invention.

Fig. 2 is a characterlstic curve.

Fig. 3 is a fragmentary diagrammatic view of a modification of the system of the character indicated in Fig. 1.

Referring to Fig. 1, that part thereof 'to the left of the line X-X represents a radio receiving set while the portion to the right of that line represents the sources of alternating current for heating cathodes or filaments of the tubes and for supplying rectified filtered alternating current to the anode or plate circuits of the tubes. Th'e'alternating current is derived from'the conductors 1 and 2, as through a plug receptacle or lamp socket 3 connecting with the transformer primary 4. inductively related to secondaries 5, 6 and 7 delivering low voltage alternating current for heating the cathodes or filaments of the vacuum tubes of the receiving set while the secondary 8 delivers current for heating the filament or cathode of the rectifier tube 9 whose anodes are connected to the terminals of thesecondary 10. The rectifier 9 and its associated filter system comprising choke coils, condensers and resistances as indicated constitute a source of current for the anode circuits of the tubes of the set, the several leads 11, 12, 13 and 14 supplying plate circuit current at different suitable voltages.

The received energy is absorbed by the antenna A or any other equivalent absorption structure, as a loop, etc. In the example illustrated between the antenna A and ground, earth or countercapacity E is connected the primary of a preferably step-up radio frequency transformer T across whose secondary is connected the tuning condenser 0 whose one terminal is connected through the stabilizing resistance R with the control electrode or grid 9 of the first amplifier tube V whose filament or cathode f is heated, as stated, by alternating current. The plate or anode a is connected through the high inductance or radio frequency choke coil 0 with the conductor 11 constituting a positive terminal of the plate circuit or B source of sectified alternating current. The path of the radio frequency component of the anode circuit current is through the variable capacity K and the primary of the preferably stepup radio frequency transformer T to the filament or cathode through the condensers k and 70 E The windings of this and subsequent transformers are preferably reversely poled as hereinafter described and are as indicated, of the step-up type, better indicated in Fig. 3 at T The secondary of the transformer T is bridged by the tuning condenser C a terminal of which is connected through a stabilizing resistance R with the grid of the tube V in whose anode circuit is connected the primary of the Preferably step-up radio frequency transformer T whose secondary is bridged by the variable tuning condenser C one of whose terminals is connected through a stabilizing resistance R with the grid of the third amplifier tube V In the plate circuit of the latter is the primary of the preferably stepup radio frequency transformer T whose secondary is bridged by the variable tuning condenser C between one of whose terminals and the grid of the detector tube V is connected the grid condenser k shunted by the leak resistance r. The cathode f of the detector is of the equipotential type heated by the heating resistance It itself heated by alternating current delivered by the aforesaid secondary 6. The cathode g is connected to earth or countercapacity and between it and the anode is connected condenser is. In the anode circuit is the primary of an audio frequency transformer T whose secondary is connected in the grid circuit of the audio frequency amplier tube V whose anode circuit is coupled by the audio frequency transformer T with the input circuit of the audio frequency amplifier tube V whose anode is connected through a condenser is with one terminal of the magnet winding of the loud speaker L, whose other terminal is connected to a suitable point upon the resistance 1" bridged across the filament of the tube V.

Inasmuch as the frequency of the alternating current supplied by the conductors 1, 2 is relatively low or of audio frequency it is desirable and customary in connection with tubes of the character described having filaments heated by the alternating current to minimize the hum, otherwise occasioned by the alternating filament-heating current, by

utilizing filaments of relatively low resistance, short and of relatively great cross-section, having large heat inertia or incapable of rapidly responding in temperature to changes in the amplitude of the heating current.

It is particularly to systems using tubes having filaments of this character that my invention is applicable, in order that there may be instantaneous control of volume or magnitude of amplification. In systems utilizing tubes whose filaments have low heat inertia, aswhen supplied by current from a battery, commonly heretofore utilized, a volume control may readily be obtained by adjusting a rheostat in the circuit of the filament. A rheostat in the circuit of a filament of high heat inertia, as when heated by alternating current, will efiect a volume control, but there is incident to such control a considerable and appreciable time lag, ren-' dering such type of control undesirable.

Furthermore, rheostatic control of a filament heated by alternating current and having high heat inertia has the further disadvantage of change in the amplitude of the heating current. With a given voltage impressed upon the plate circuit, the tube will be operated on such portion of its characteristic that there will occur detector action or a modulation of the radio frequency current undergoing amplification at a frequency corresponding to that of the alternating filament-heating current. This may be understood by reference to Fig. 2 which is a characteristic curve whose ordinates are, for a given plate circuit voltage, plate currents, and whose abscissae are filament temperatures. Ordinarily and desirably the tube operates on the straight part of the characteristic between such points as d and e, which implies and necessitates that the temperature of the filament shall not be materially varied as would be occasioned by adjustment of a filament rheostat. If the temperature is reduced the tube would act upon that part of the characteristic a portion at least of which would extend into the curved region to the left of the point d, or if the temperature were increased, to the right of the point e, and in either case there would be a detector action or modulation of the radio frequency current, substantially at a frequency corresponding to that of the filament-heating current, thereby causing an undesired hum accompanying the reproduction of speech, music, etc., by the signal translating instrument or loud speaker L.

Instantaneous control of volume with avoidance of the production of the hum just referred to is available by utilizing; the varivariable in steps and comprises a series of two or more fixed condensers any number of which may be brought into series with each other in a connection between anode a of the tube V and the manually operable switch S connected to one terminal of the primary of the transformer T trated there are provided six fixed condensers 0 I0 k is", 70 and Ia whose capacities may be of the order, when the receiving set is designed for reception of Wave lengths ranging from about 200 to about 600 meters, 700, 500, 250, 125, 4:0 and 10 micro micro farads, respectively whereby as the'switch S is moved in clockwise direction the capacity in series between the anode a of the tube V andthe primary of the transformer T is diminished in suitable steps.

When maximum amplification is desired the switch S will cut out all of the condenser elements of the capacity K and the volume of reproduction or amphfication will be progressively reduced as the switch S is moved in clockwise direction.

As indicated in Fig. 3 a smoothly variable capacity K may be utilized in lieu of the capacity K of Fig. 1. However, a smoothly variable capacity having a range of the character indicated for the capacity K is volumi- 1 nous and expensive, requiring considerable room in a compactly arranged receiving set. By utilizing capacity in steps as indicated in Fig. 1 however the several condensers k to is are individually and collectively small and occupy but slight space, and are relatively inexpensive.

The capacity K or K introduces reactance into the anode circuit, thereby reducing the voltage effectively impressed upon the primary of the coupling transformer'T, and so reducing the amplification effected by the subsequent tubes. The reactance K or K also has the effect, where the input and outputsystems are tuned as described, of in effect introducing resistance into the input system tuned by the condenser C thereby further reducing the amplification as effected by the tube V and the succeeding tubes.

The described'location of the condensers'K or K between the anode a of the tube V and the high potential terminal of the coupling v means, which in the example illustrated is the primary of the transformer T is preferable and of advantage in that distributed capacity between the condenser K or K and ground or countercapacity E does not disturb or materially' affect the .relation of the reactance of the control condenser K or K to the reactance of the coupling means such as the primary of the coupling transformer T Such distributed capacity as is present in effectively in shunt to bOtllrthB volume control condenser K or K and the coupling means, as pri- In the example illus-' capacity adjustment.

In the arrangement indicated, and especially where the parts are assembled in a compact set there occurs natural or inherent coupling capacity between various stages and particularly between, for example, the grid or grid circuit of the tube V and the grid or gridcircuit of the tube V. To the grids of these neighboring tubes are connected for example the stators of the tuning condensers C and C and between these condenser stators, and/or between other-conductive bodies con nected to the neighboring grids, exists an inherent coupling capacity tending to instability or production of oscillations. This is .more or less completely overcome by the reversed poling of the windings of the transformer T in such wise that the grid end of the secondary and the anode terminal of'the primary of this transformer are at opposite radio frequency polarities. In the grid leads of the radio frequency amplifier tubes are disposed suitably high resistances R which further contribute to stabilization.

In a system where the capacitative coupling is more or less neutralized through another capacity, in the present instance inherent or natural capacity between neighboring grid circuits for example, the employment of capacity reactance is efiective for volume control without material effect upon or disturbance of the necessary neutralization for either external couplings or coupling through the grid-plate capacity.

While there has been described the utilization of but a single volume control capacity K or K it will be understood that a similar capacity similarly located may be utilized in one or more of the subsequent stages; and while the control capacity has been described as associated with the output circuit or system of the first amplifier tube of the series it will be understood that it may be associated with the output circuit or system of any other stage. i

In a set of the character described, besides the tuning adjustment or adjustments, there pling it substantially solely electromagnetically to another circuit, and a variable capacity in series with said means in said output circuit adjustable throughout its range for controlling volume without decrease bility of the amplifier.

2. The combination with a stabilized thermionic amplifier having input and output circuits, of means in the output circuit for coupling it substantially solely electromagnetically to another circuit, and a variable capacity in series with said coupling means between its high potential terminal and the anode of said amplifier adjustable throughout its range for controlling volume Without decrease of stability of the amplifier.

SARKES TARZIAN.

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